Children with cystic fibrosis often exhibit poor growth patterns and experience malnutrition as a result of pancreatic insufficiency. A number of studies have reported decreased bone density in patients with cystic fibrosis relative to their healthy peers. Furthermore, cystic fibrosis is associated with demineralization abnormalities such as delayed puberty, estrogen deficiency, and possibly chronic respiratory acidosis. However, current research shows that bone density is significantly related to extrinsic factors such as calcium intake, Vitamin D intake, and level of physical activity. This cross-sectional study will examine differences in bone density between patients with cystic fibrosis and healthy controls, and will examine the association between physical activity and bone mineral density in both children and adolescents with and without cystic fibrosis.